Interfacial Step Research Articles

Ultrafast Hole Trapping in Te-MoTe2-MoSe2/ZnO S-Scheme Heterojunctions for Photochemical and Photo-/Electrochemical Hydrogen Production.

Te-MoTe2-MoSe2/ZnO S-scheme heterojunctions are engineered to ascertain the advanced redox ability in sustainable HER operations. Photo-physical studies have established the steady state transfer of photo-induced charge carriers whereas an improved transfer dynamics realized by state-of-art ultrafast transient absorption and irradiated-XPS analysis of optimized 5wt% Te-MoTe2-MoSe2/ZnO heterostructure. 2.5, 5, and 7.5wt% Te-MoTe2-MoSe2/ZnO photocatalysts (2.5MTMZ, 5MTMZ and 7.5MTMZ) exhibited 2.8, 3.3, and 3.1-fold higher HER performance than pristine ZnO with marvelous apparent quantum efficiency of 35.09%, 41.42% and 38.79% at HER rate of 4.45, 5.25, and 4.92 mmol/gcat/h, respectively. Electrochemical water splitting experiments manifest subdued 583 and 566 mV overpotential values of 2.5MTMZ and 5MTMZ heterostructures to achieve 10 mAcm-2 current density for HER, and 961 and 793 mV for OER, respectively. For optimized 5MTMZ photocatalyst, lifetime kinetic decay of interfacial charge transfer step is evaluated to be 138.67 ps as compared to 52.92 ps for bare ZnO.

Cycling performance of Li metal anode in localized high concentration electrolyte and dynamic mechanism analysis

In this work, we investigated the apparent cycling performance of lithium metal at different chemical compositions and series current densities; examined the microscopic morphology and thickness variation of the deposition layer on the surface of lithium metal anode and the concentration-depth distribution of trace elements in the solid electrolyte interphase (SEI) film; and characterized the kinetic behavior and features of the elementary steps (mass transfer, charge transfer, electro-crystallization) at Li-electrolyte interface using microelectrode technology and various electrochemical test methods. The results show that the lithium metal anode has better cycling performance in high concentration and localized high concentration electrolyte. At the same time, the experimental results confirm that the formation of spherical crystal nucleus is favored only under certain chemical conditions and certain reaction rate; under these conditions, the induction period and the self-smoothing process of critical crystal nucleus can be found. It suggests that there are determined causal among the apparent performance of lithium metal anode, the kinetic parameters of the interfacial charge transfer step and the electro-crystallization step, and these correlations can be used as a reference for screening and evaluating electrolyte systems and battery operating conditions, providing a reliable kinetic basis for future work.

Atomically Dispersed Manganese Lewis Acid Sites Catalyze Electrohydrogenation of Nitrogen to Ammonia

Atomically Dispersed Manganese Lewis Acid Sites Catalyze Electrohydrogenation of Nitrogen to Ammonia

The Effects of the Solvent Choice of the Continuous Phase on the Poly(Urea-Urethane) Microcapsules Properties

Xylitol, a natural crystalline polyol, presents a cooling effect due to its negative heat of solution at 35 °C supported by humidity absorption, contributing to a fresh sensation when it dissolves. Since this material is sometimes in a liquid state, it cannot be incorporated in or onto a substrate without being protected. One of the strategies to protect the active substance may be forming a barrier layer at its surface, i.e., microencapsulation. The present work is devoted to studying the effect of continuous phase parameters affecting on encapsulation of xylitol with a poly (urea-urethane) shell through a two-step microencapsulation process. The first step is liquid-liquid dispersion either in toluene or Miglyol 812N, and the second step is microencapsulation by interfacial polymerization. The process can be used to control the size distribution of the microparticles, the thickness, and the chemical nature of the shell, which influences the release rate of the active substance. The choice of the continuous phase solvent (toluene or Miglyol 812N) required some changes in the formulation of the system, especially the HLB of the surfactant mixture, to obtain a stable emulsion with a narrow particle size distribution. The thermo-chemical and morphological characteristics of microparticles were studied by Fourier transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), enthalpy of dilution, and scanning electron microscope (SEM). The microparticle size is governed by the emulsion step and the chemical composition of the organic phase. Most of the thermal properties are related to their porous structure and their chemical shell formation during the interfacial polymerization step.

The influence of SiO2 and Al2O3 nanofluids based on seawater on IFT reduction: EOR

Water injection is a widespread technique used in the oil production sector to enhance the oil recovery and expand the production life of a well. Using nanoparticles to further enhance the recovery by reducing interfacial tension (IFT) and altering wettability is a new trend adopted in the water injection application due to the low risk of formation damage, also for their cost-effectiveness. However, water salinity and suspended particles are significant challenges as they affect the behaviour of nanoparticles in the water saline media. The objective of this study is to evaluate the effect of two types of nanofluids with nano-SiO2 and Al2O3 on reducing IFT for water injection application. In this work, a 1:1 mix of seawater and effluent water is, respectively, examined based on an interfacial step change. The technique of mixing seawater with effluent water is being used to reduce the salinity of the effluent water for the selected reservoir. The mixed water was prepared under elevated temperature and 1000 Psi to resemble downhole conditions and then evaluated by inductively coupled plasma and energy-dispersive spectroscopy, where for thermal stability prediction of the water mix the OLI Studio was used. Then selected nanoparticles were then added at different concentrations to the mixed water to form the required nanofluid. IFT was measured as a function of nanoparticle concentration by a Drop Shape Analyzer—DSA100 apparatus using an optical pendant drop method to evaluate the effect of the nanoparticles within the prepared mix in terms of interfacial tension between crude oil and the prepared water, as IFT is an essential variable for oil recovery. The study revealed that 0.025 and 0.05 wt% of SiO2 concentration had reduced the IFT of the crude effectively for the selected seawater mix ratio. In addition, when R2 values for the collected data were compared, Al2O3 concentration of 0.025% showed more cost-effectiveness over other concentrations. The study concludes that the prepared water mix is compatible with nanoparticles and causes the desired reduction in IFT at a low concentration which can be considered as an advantage in terms of cost-effectiveness and rock pore plugging.

Relationship between interfacial and foaming properties of a Porphyra dioica seaweed protein concentrate

Porphyra dioica macroalgae can be regarded as a food-grade protein source that can be used for the stability of dispersed food systems. This work is focused on the foaming properties of a seaweed protein concentrate (SWE) from Porphyra dioica . The characterisation of air-water (A/W) interfacial layers formed after the SWE adsorption was carried out by means of interfacial tension, interfacial viscoelastic measurements and step deformation tests. These results were related to those obtained for SWE stabilized foams. Interfacial shear measurements indicate that not extensive protein-protein interactions at the A/W interface were developed (G' s = 1.0 ± 0.1·10 −2 mPa m), whereas the dilatational response (E' s = 23.5 ± 0.5 mN/m) match with the formation of a rigid interface as a result of a densely packed structure. Even if the foaming properties obtained for SWE (overall foam capacity, OFC, = 0.74 ± 0.01 mL/s) are similar to those reported for other commercial protein systems, its lower stability (t 1/2 = 204 ± 4 s) would indicate the need of adding stabilizers for an adequate shelf life of the final food product. The suitability of combining dilatational and interfacial shear rheology to predict the dynamics of dispersed systems was proven to be relevant to acquire insights of complex interfaces. • Porphyra dioica algae could be a food-grade protein source for dispersed systems. • Dilatational response indicated the formation of a rigid interface. • The weak interfacial shear response suggested the formation of a densely packed structure. • Dilatational and interfacial shear rheology was combined to predict the dynamics of foams. • Foaming properties were similar to those reported for commercial protein systems.

Contact barriers modulation of graphene/β-Ga2O3 interface for high-performance Ga2O3 devices

The ultra-wide-gap β-Ga2O3 has been regarded as a promising material for next-generation power electronic and deep-ultraviolet (UV) photodetectors. Exploring a suitable electrode is vital for realizing high performance β-Ga2O3 based nanodevices. Herein, the structural and contact properties of graphene/Ga2O3 interfaces are tuned and investigated by using the first-principles calculations. Results show that the small n-type Schottky barrier of about 0.07 eV for the graphene/Ga2O3 interface with weak interlayer interaction is irrespective of the interface stacking arrangement. Moreover, the intrinsic electronic property of Ga2O3 is well preserved in the interface. More interestingly, the n-type Schottky barrier to Ohmic contact transition can be obtained by shorting the interlayer distance, or increasing the graphene layers or applying a negative external electric field for the interface. Moreover, applying a large positive external electric field can realize the p-type Schottky barrier to Ohmic contact transition for graphene/Ga2O3 interface. These results are uncovered by analyzing the interfacial dipole and potential step of graphene/Ga2O3 interface, and expected to enhance the application potential of graphene electrode in the β-Ga2O3 based electronic and optoelectronic devices.

Covalent organic framework incorporated outer-selective hollow fiber thin-film nanocomposite membranes for osmotically driven desalination

In this study, new outer-selective hollow fiber (OSHF) thin film nanocomposite (TFN) forward osmosis (FO) membranes incorporated with amine-rich Schiff-based network (SNW-1) nanoparticles (NPs), a type of covalent organic frameworks (COFs), were developed by vacuum-assisted interfacial polymerization (VAIP). The SNW-1 NPs possess hydrophilic nature and porous internal structures, which are desirable for producing highly permeable and efficient FO membranes. SNW-1 NPs were conformally packed across the outer surface of the HF substrate by vacuum pressure applied during the VAIP process leading to defect-free coatings. Furthermore, covalent bonding between secondary amine (NH2−) groups across the SNW-1 network and remanent carboxylic groups present from the monomer used for the interfacial polymerization step supported the adhesion of SNW-1 NPs to the native poly(amide) layer present across the TFN membrane surface. As a result, SNW-1 loading at 0.001 wt% exhibited the best FO performance with enhanced water flux more than 23% of the pristine one (31.5 L m−2 h−1) and relatively low specific reverse solute flux (SRSF, Js/Jw) at 0.18 g L−1 using 1 M NaCl and DI water in series of TFN composite membranes. The optimum loading at 0.001 wt% was much lower than those in other home-made TFN membranes (normally above 0.05 wt%) due to the minimum loss of SNW-1 in the VAIP. Also, the TFN membrane offered excellent FO operation stability tested for 72 h. Such novel approach is promising to optimize FO processes for desalination and water treatment in the future.

Effect of Surface States and Breakdown of the Schottky–Mott Limit of Graphene/Silicon van der Waals Heterostructure

Recent experimental studies have often described the interface of the graphene/semiconductor (G/S) junction in terms of conventional metal/semiconductor (M/S) contact models, but the details of the charge transfer mechanism remain unclear. Here, density functional theory calculations are used to investigate the graphene/silicon (G/Si) interface in the absence and presence of different surface states of the doped Si substrate. It is confirmed that the interaction between graphene and the Si surface is of van der Waals (vdW) type, even though the Si surface is shown to have a high density of dangling bonds. We show that the metallic surface state transfers its spilled-out electron to graphene but prevents the development of a depletion region of free carriers in the subsurface region of the substrate due to strong electrostatic screening property of the metallic surface state, while the hole doping in graphene by the electron-trapping surface states is inhibited by the interfacial potential step of the pillow effect. In the absence of surface states, the behavior of transferred charges is quite free in the interfacial layer; thus, the effective distance of a simple plane capacitor model of the charge transfer potential should be treated as a variable instead of fixing it as in the conventional M/S interface models. More interestingly, the sensitivity of the Schottky barrier height of the G/Si vdW interface can overcome the Schottky–Mott limit and the recently proposed barrier models due to the dependence of the charge transfer potential on the Fermi level shift in graphene.

Encapsulating an organic phase change material within emulsion-templated poly(urethane urea)s

Interfacial step growth polymerization within oil-in-water high internal phase emulsions was used to synthesize poly(urethane urea) monoliths, consisting of 90% organic phase change material encapsulated within micrometer-scale capsules, for thermal energy storage and release applications.

Heterobinuclear Light Absorber Coupled to Molecular Wire for Charge Transport across Ultrathin Silica Membrane for Artificial Photosynthesis.

Coupling of robust, all-inorganic heterobinuclear light absorbers to metal oxide catalysts for water oxidation across an ultrathin product-separating silica membrane requires charge transfer through organic molecular wires embedded in the silica. A synthetic approach for assembling the bimetallic units on the silica surface is introduced that is compatible with the presence of encapsulated organic molecules. Accurate selection and fine tuning of the concentration of embedded conducting wires are enabled by a two-step method consisting of surface attachment of a tripodal anchor, trimethoxysilyl aniline, followed by attachment of p-oligo(phenylene vinylene) through amide linkage. Each step of the assembly process was monitored and characterized by a combination of Fourier transform infrared, Fourier transform-Raman, and UV-vis spectroscopy techniques. Hole transfer was observed from transient CoIII, formed by TiIVOCoII → TiIIIOCoIII charge transfer excitation of the chromophore, to p-oligo(phenylene vinylene) molecule within the 8 ns width of the photolysis laser pulse by transient optical absorption spectroscopy of the wire radical cation. The rectifying property of the light absorber-wire assembly enabled by appropriate selection of redox potentials of metals and embedded wire obviates the need for a molecularly defined linkage between the components. Combined with the previously observed ultrafast hole injection from the embedded wires to Co oxide catalyst, the result implies visible-light-induced hole transfer from visible-light-excited binuclear light absorber to water oxidation catalyst across the silica separation membrane in a few nanoseconds or faster. Demonstration and understanding of this interfacial charge-transfer step is critical for developing nanoscale core-shell architectures for complete photosynthetic cycles.

Novel small-molecule zwitterionic electrolyte with ultralow work function as cathode modifier for inverted polymer solar cells

Abstract Interfacial compatibility between the electrode and organic semiconductor plays a critical role in controlling the charge transport and hence efficiency of organic solar cell. Here, we introduce a novel small-molecule zwitterionic electrolyte (S1) combined with ZnO as electron transporting interlayer employed for the inverted PTB7:PC71BM bulk heterojunction solar cell. The resulting device with the S1/ZnO stacked interlayer achieves a high PCE of 8.59%, obtaining a 16.2% improvement over the control device performance of 7.4% without the S1 attributed to the significant increased short-circuit current density and fill factor. The interfacial properties are investigated. It is found that the S1/ZnO interlayer possess an ultralow work function of 3.6 eV, which originates from the interfacial double dipole step induced by the zwitterionic side chain electrostatic realignment at interface. The S1/ZnO interlayer exhibits the excellent charge extraction ability, suppresses the charge recombination loss and decreases the series resistance at the active layer/electrode contact.

The Effect of Oxygen Uptake on Charge Injection Barriers in Conjugated Polymer Films.

The energy offset between the electrode Fermi level and organic semiconductor transport levels is a key parameter controlling the charge injection barrier and hence efficiency of organic electronic devices. Here, we systematically explore the effect of in situ oxygen exposure on energetics in n-type conjugated polymer P(NDI2OD-T2) films. The analysis reveals that an interfacial potential step is introduced for a series of P(NDI2OD-T2) electrode contacts, causing a nearly constant downshift of the vacuum level, while the ionization energies versus vacuum level remain constant. These findings are attributed to the establishment of a so-called double-dipole step via motion of charged molecules and will modify the charge injection barriers at electrode contact. We further demonstrate that the same behavior occurs when oxygen interacts with p-type polymer TQ1 films, indicating it is possible to be a universal effect for organic semiconductors.

Fabrication and characterization of temperature and pH resistant thin film nanocomposite membranes embedded with halloysite nanotubes for dye rejection

In this study, nanofiltration (NF) membranes with high pH and temperature resistance were fabricated by introducing halloysite nanotubes (HNTs) into the organic phase during the interfacial polymerization step. HNTs were dispersed in cyclohexane with the concentration 0% (TFN0), 0.02% (TFN0.02), 0.04% (TFN0.04) and 0.06% (TFN0.06) as w/v (%). Fabricated membranes were characterized by FT-IR spectroscopy, SEM and AFM analyses, optical profilometry, contact angle and zeta potential measurements. Filtration performance tests were conducted with 2000ppm MgSO4 and NaCl solutions and 100ppm of synthetic dye solutions (Setazol Red Reactive and Reactive Orange dyes), respectively. For pH-resistance tests, synthetic dyes were filtrated in acidic, neutral and base conditions (pH=4–7–11) to measure changes in flux and rejection. The effect of the temperature of the feed stream on membranes were determined by the filtration of pure water and dye solutions at 15°C, 25°C and 40°C. Among different membranes fabricated with varying HNTs content, TFN0.04 membrane showed increased water flux without considerable salt and dye rejection loss.

Describing Ion Exchange at Membrane Electrodes for Ions of Different Charge

AbstractIt is well‐documented in the literature that the Nikolsky‐Eisenman equation cannot accurately describe the equilibrium of ion exchange at membrane electrodes for ions of different charge. Despite this, unfortunately, it is still widely used owing to the complexity of the more rigorous formalism developed by Bakker et al. in 1994. Here, different available approaches are presented in a unified manner and compared. This includes two different approximations that are equally appropriate for cases of low level of interference where the extent of ion‐exchange is comparatively small, one of which is introduced here for the first time. The comparison also considers the permutated form of the Nikolsky‐Eisenman equation, where the primary ion is treated as the interfering ion and vice versa. As the permutated form gives a deviation from the thermodynamic model that is opposite that of the regular Nikolsky‐Eisenman equation, the two can be combined to give a semi‐empirical equation that is surprisingly close to the thermodynamic model and that comprises a single equation for any charge combination. The different choices presented here may be helpful to solve more complex theoretical problems, as for example in the modeling of the time dependence of the electrode response by numerical simulation where the interfacial step condition is a unique and difficult feature of the calculation.

Femtosecond Charge-Injection Dynamics at Hybrid Perovskite Interfaces.

With a power conversion efficiency (PCE) exceeding 22 %, perovskite solar cells (PSCs) have thrilled photovoltaic research. However, the interface behavior is still not understood and is a hot topic of research: different processes occur over a hierarchy of timescales, from femtoseconds to seconds, which makes perovskite interface physics intriguing. Herein, through femtosecond transient absorption spectroscopy with spectral coverage extending into the crucial IR region, the ultrafast interface-specific processes at standard and newly molecularly engineered perovskite interfaces in state-of-the-art PSCs are interrogated. Ultrafast interfacial charge injection occurs with a time constant of 100 fs, resulting in hot transfer from energetic charges and setting the timescale for the first step involved in the complex charge-transfer process. This is also true for 20 % efficient devices measured under real operation, for which the femtosecond injection is followed by a slower picosecond component. These findings provide compelling evidence for the femtosecond interfacial charge-injection step and demonstrate a robust method for the straightforward identification of interfacial non-equilibrium processes on the ultrafast timescale.

Thermostatics of Concentration Polarization and the Possible Effects of Surface Ad-Ions in SOFC Composite Cathodes

In situations common to high-temperature SOFC (Solid-Oxide Fuel Cell) operation at steady-state, the dependence of the activity of oxide ions on the oxygen partial pressure (p_O2) becomes relatively unimportant for p_O2>0.15 bar. Nevertheless, one might question what would be the indirect effect (if any) of surface ad-ions on the evaluation of concentration polarization due to changes on the oxygen partial pressure near to the grain boundary between electronic, ionic, and gas phases. From thermostatics considerations and macroscale-continuum phenomenological equations it is shown that the definition of concentration polarization, as commonly found in the literature, may contain a series of limitations and, among these limitations, it is discussed the relative importance of oxygen surface ad-ions on the formation of concentration cells,when it is compared to the concentration gradients of “bulk” gas species in the porous channels of SOFC cathodes. This theoretical discussion about the influence of contact chemistry near the TPB (three-phase boundary) region indicates that concentration polarization could in fact either increase or decrease, depending on whether the chemical activity of oxide ions is affected by the local chemical activity of O2 near the gas/solid interface. In order to verify this, one needs to know how the differences of interfacial potential step and chemical activity relate to changes in the contact chemistry and space charge zone near this interface. Particularly, the evaluation of the potential step between the electronic conductor and the ion adsorbed layer requires the prescription of certain phenomenological parameters. In the present study, one of these parameters is the density of “active” surface sites near the TPB region, which represents just a fraction of the total surface site density available over the entire electrode phase. It is a fraction because only those sites sufficiently close to the TPB “hot spot” are considered “active” for the adsorption of charged species, which are then subsequently able to undergo electrochemical reduction at the TPB. So to calculate this density of “active” surface sites and thus the corresponding electrostatic potential step, a phenomenological governing equation for oxygen ad-ions on the electrode surface is proposed (i.e., in terms of surface coverage of ad-ions) to account for electrocatalytic and interfacial transport processes (i.e., competing surface diffusion and adsorption processes near the TPB “hot spot”) within a composite porous cathode.

High-resistivity sol-gel ITO thin film as an interfacial buffer layer for bulk heterojunction organic solar cells

Bulk heterojunction organic solar cells have been fabricated by inserting a high-resistivity sol-gel ITO buffer layer between an ITO anode and a PEDOT:PSS hole injection layer. The performance of the devices with the sol-gel ITO atop the ITO anodes treated by conventional annealing at 500 °C for 1 h and rapid thermal process (RTP) at 800 °C for 20 and 30 s was compared. The best power conversion efficiency of 3.5% was achieved for the device with the 15-nm-thick sol-gel ITO treated with RTP at 800 °C for 30 s, as compared with 2.7% of the standard device under an illumination of AM 1.5. In addition, the short circuit current of the device was significantly increased by 42.7%. The observed enhancement of the short circuit current can be attributed an interfacial energy step created by the high-resistivity sol-gel ITO between the ITO anode and the PEDOT:PSS.

Effect of the Dianhydride/Branched Diamine Ratio on the Architecture and Room Temperature Healing Behavior of Polyetherimides.

Traditional polyetherimides (PEIs) are commonly synthesized from an aromatic diamine and an aromatic dianhydride (e.g., 3,4'-oxidianiline (ODA) and 4,4'-oxidiphtalic anhydride (ODPA)) leading to the imide linkage and outstanding chemical, thermal and mechanical properties yet lacking any self-healing functionality. In this work, we have replaced the traditional aromatic diamine by a branched aliphatic fatty dimer diamine (DD1). This led to a whole family of self-healing polymers not containing reversible chemical bonds, capable of healing at (near) room temperature yet maintaining very high elastomeric-like mechanical properties (up to 6 MPa stress and 570% strain at break). In this work, we present the effect of the DD1/ODPA ratio on the general performance and healing behavior of a room temperature healing polyetherimide. A dedicated analysis suggests that healing proceeds in three steps: (i) an initial adhesive step leading to the formation of a relatively weak interface; (ii) a second step at long healing times leading to the formation of an interphase with different properties than the bulk material and (iii) disappearance of the damaged zone leading to full healing. We argue that the fast interfacial adhesive step is due to van der Waals interactions of long dangling alkyl chains followed by an interphase formation due to polymer chain interdiffusion. An increase in DD1/ODPA ratio leads to an increase in the healing kinetics and displacement shift of the first healing step toward lower temperatures. An excess of DD1 leads to the cross-linking of the polymer thereby restricting the necessary mobility for the interphase formation and limiting the self-healing behavior. The results here presented offer a new route for the development of room temperature self-healing thermoplastic elastomers with improved mechanical properties using fatty dimer diamines.

A combined interfacial and in-situ polymerization strategy to construct well-defined core-shell epoxy-containing SiO2-based microcapsules with high encapsulation loading, super thermal stability and nonpolar solvent tolerance

ABSTRACTSiO2-based microcapsules containing hydrophobic molecules exhibited potential applications such as extrinsic self-healing, drug delivery, due to outstanding thermal and chemical stability of SiO2. However, to construct SiO2-based microcapsules with both high encapsulation loading and long-term structural stability is still a troublesome issue, limiting their further utilization. We herein design a single-batch route, a combined interfacial and in-situ polymerization strategy, to fabricate epoxy-containing SiO2-based microcapsules with both high encapsulation loading and long-term structural stability. The final SiO2-based microcapsules preserve high encapsulation loading of 85.7 wt% by controlling exclusively hydrolysis and condensed polymerization at oil/water interface in the initial interfacial polymerization step. In the subsequent in-situ polymerization step, the initial SiO2-based microcapsules as seeds could efficiently harvest SiO2 precursors and primary SiO2 particles to finely tune the SiO2 wall thickness, thereby enhancing long-term structural stability of the final SiO2-based microcapsules including high thermal stability with almost no any weight loss until 250°C, and strong tolerance against nonpolar solvents such as CCl4 with almost unchanged core-shell structure and unchanged core weight after immersing into strong solvents for up to 5 days. These SiO2-based microcapsules are extremely suited for processing them into anticorrosive coating in the presence of nonpolar solvents for self-healing application.